Both players have since had successful operations on similar shoulder injuries but their regional coach doesn't believe they will be fit in time for the start of the November internationals.
Wales play the first of four autumn Tests on November 7, with former Lions star Dai Young believing that the clash with the All Blacks will come two or three weeks too soon.
"The middle to end of November is maybe more realistic," said Young, who toured three times with the Lions in 1989, 1997 and 2001.
"With these injuries you don't know. Everyone reacts a bit differently to similar operations and it's early days in their rehab."
Following the game against New Zealand, who are led by former Wales and Lions coach Graham Henry, Wales take on Samoa, Argentina and Australia at the Millennium Stadium in Cardiff.
And while Jenkins and Williams look set to join Ospreys and Lions prop Adam Jones in the stands for at least the first couple of autumn internationals, there was better news for fellow Lions Andy Powell and Leigh Halfpenny.
Having returned home early from South Africa with a leg injury, Halfpenny will start the Blues' Magners League encounter against Munster at Thomond Park tomorrow after being involved against Edinburgh last weekend.
And No8 Powell, who, like Halfpenny, became a Lion in his first season of international rugby is set to feature from the bench against the reigning Magners League champions in what will be his first appearance since returning from South Africa.